java - 为什么我收到 java.lang.StringIndexOutOfBounds 异常？

Question

我有一个程序，它接受两个字符串参数，并根据它们的索引将它们视为 int，并尝试像我们在纸上所做的那样进行加法，但我收到 java.lang.StringOutOfBounds Exception ，我无法解决它如有任何帮助，请提前致谢

import java.util.Arrays;

public class Algorithm {
    boolean flag=false;

    public void topla(String str1,String str2){

        String temp="";
        int sum1=0,sum2=0;

        String sonuc1="";
        if(str2.length()>str1.length()){
            temp=str1;
            str1=str2;
            str2=temp;

        }

         for (int i=0; i<str1.length(); i++)
         {
             sum1 = Integer.parseInt(str1.substring(str1.length()-1-i, 1));
             sum2=0;
             if(str2.length()-i>0){
                 sum2=Integer.parseInt(str2.substring(str2.length()-1-i,1));
             }
             else
                 sum2 = 0;
             sum1 = sum1 + sum2;
             if(flag)
             {
                 sum1 += 1;   
                 flag = false;
             }
             if (sum1 > 9)    
             {
                 flag = true;
                 sum1 -= 10;
             }
             sonuc1 += sum1;
         }
         char[] sonucu_duzelt = sonuc1.toCharArray();
         String string =new String(sonucu_duzelt);
         System.out.println(string);
         }

Answer 1

让我们看看substring方法的实现:

public String substring(int beginIndex, int endIndex) {
    if (beginIndex < 0) {
        throw new StringIndexOutOfBoundsException(beginIndex);
    }
    if (endIndex > value.length) {
        throw new StringIndexOutOfBoundsException(endIndex);
    }
    int subLen = endIndex - beginIndex;
    if (subLen < 0) {
        throw new StringIndexOutOfBoundsException(subLen);
    }
    return ((beginIndex == 0) && (endIndex == value.length)) ? this
            : new String(value, beginIndex, subLen);
}

这段代码对您很重要:

int subLen = endIndex - beginIndex;
if (subLen < 0) {
    throw new StringIndexOutOfBoundsException(subLen);
}

您必须更改以下行:

Integer.parseInt(str1.substring(str1.length()-1-i, 1));
Integer.parseInt(str2.substring(str2.length()-1-i,1));

str1.length()-1-i 不能大于1。当i等于(length - 1)时，str1.length()-1-i等于0。因为0 < 1， Jvm 抛出 new StringIndexOutOfBoundsException()。